Examples are known in the state of techniques of bearing groups for a flanged hub for driving wheels in motor vehicle applications. The document EP 2602123 A1, for example, describes an asymmetrical hub bearing unit for the wheel of a motor vehicle. The hub bearing unit in this example includes a flanged hub rotatable around a rotation axis, a flange integral with the hub flanged and transverse to the axis of rotation, a stationary ring disposed radially outside of the flanged hub and provided with rolling tracks axially spaced from one another, and two rolling bodies crowns (for example, balls) arranged between the stationary ring and the flanged hub. The flanged hub integrally forms a radially inner raceway for the ball bearing axially outer, while the radially inner raceway for the balls axially inner crown is formed on an inner ring of the bearing, radially outer planted on flanged hub.
Such a realization, especially in the case of heavy duty applications in terms of load transmitted, entails considerable local loads between the bearing rings and rolling bodies. Also, it does not permit obtaining large values of resistance of the bearing and its greater duration in time. Finally, it usually presents important axial dimensions because of the presence of a flange integral to the flange portion and the hub transverse to the axis of rotation.
To increase the performance and especially the stiffness of the bearing, an increase in the distance of the pressure centers is required. This can be achieved by increasing the diameter of the circumference of the centers of the rolling bodies (the so-called “pitch diameter” or more simply “pitch”) of the bearing. Such solutions are already known and are developed in order to significantly improve the performance. The disadvantage connected to the increase of the “pitch” is that consequently also the volume and therefore weight dramatically increases with the “pitch-squared value”. This increase in weight usually cannot be accepted by car manufacturers.
Another improvement involves further increasing the diameter of the circumference of the centers of the rolling bodies so as to be able to enter inside the bearing constant velocity joint and integrate in a single piece the so-called bell of the joint with the hub, or with the inner ring of the bearing. Evidently, the integration of both components allows the reduction of weight and cost of the entire unit and makes it possible to further reduce weight and costs by also integrating the small inner ring of the bearing, the axially internal, with the bell of the joint. In other words, the hub also assumes the function of single inner ring of the bearing and the bell of the joint at a constant speed.
The concept of a single inner ring is already known in so-called third-generation bearings. The main difference as compared to the other known solutions exists in the fact that the bearing has an axial clearance, which is not axially preloaded. This feature, in the past, has been accepted for standard applications with no particularly heavy load conditions, and also because the bearing design did not allow the generation of no axial preload. With the development of applications that require high performance, this situation is no longer acceptable and the bearing must necessarily be axially preloaded.
There exists, therefore, the need to develop a method for preloading a bearing hub unit with high performance.